Pyrex discs 5" and 10"

[Stefan Buda]

I would buy new but no one sells them any more.
I prefer thin ones and old chipped mirrors would suit too if there is enough thickness left for machining down to 25 mm for the 10" and 15 mm for the 5".

[JohnF]

I may have a 10 inch mirror for sale-- just purchased another one, as my telescope had lost its aluminium coating. But so not know if my mirror is Pyrex. Have to try out the new Second hand one first -- Don't know its F number. Old one is about f5.

[Stefan Buda]

Hi John,

Have a look at the colour of the disc from the side. If it is greenish then it is plate glass if it is a bit yellow then it is most likely Pyrex.

Also I can re-coat your secondary but, when adding on the postage, it would cost as much as buying a new one.

Cheers,
Stefan

[Rod]

Hi Stefan

I have a full thickness Pyrex 10 inch blank you are welcome to. I can bring it to ASV Instrument Making next week.

Rod

[Stefan Buda]

Hi Rod,

Bring it in please. I'll think about it, maybe I'll slice it down to a useful thickness. It shouldn't be as difficult as the 16" was. :lol:

Stefan

[JohnF]

It is 45MM thick. And it has some white inclusions in the glass -- think it was cast in that glass. Will look for any other colour.



If all else fails, will redcoat in silver -- Tollen's test for Aldehyde

-- https://www.youtube.com/watch?v=D1_-Xc2SpyE

[Stefan Buda]

In that case I can't use it because chances are that those inclusions will end up right on the surface once I cut it down to a good thickness.
Thanks anyway.

[JohnF]

By the way, slight yellow tinge -- NOT Green.

10 1/4 inch diameter. But I may make a scope later from it.

[roddz]

Up to what size mirrors can you recoat?
I have a 16" mirror that needs recoating.

Rodd

[sfarndell]

Hi Stefan

I have a few pieces of glass lying around:

100mm plate glass 20-25mm thick picked up because one never knows when that will be useful. After 5 years it's still a paperweight so can go to a new home.


150mm diameter water-cut piece of plate glass 10mm thick that I was going to turn into a schief at some point in life. 2 paperweights are excessive so this just lives in a drawer...


I also have a 16" which needs a new coating if you can recoat a mirror that size!

Thx
Scott

[Stefan Buda]

Thanks Scott,

I need them to be Pyrex as they are for making CDK astrographs.
Pyrex is no longer made, so I'm collecting old blanks.

Recently I acquired an old school 10" blank from a fellow ASV member, and I'm in the process of slicing it into two discs - one 25mm thick and one 15mm thick. I will be able to cut two secondary discs from the thinner one.

[Saturnine]

Hi

Sent an PM earlier Stefan.